We are investigating the mechanism by which the 60,000 dalton product of the Rous sarcoma virus src gene (p60src) effects cellular transformation. p60src is a protein kinase with the unusual specificity of phosphorylating tyrosine. Our efforts will concentrate on identifying the intracellular targets of this protein kinase. This task will be aided by the fact that any substrate of p60src should contain the rare modified phosphoamino acid phosphotyrosine. We will also attempt to determine how phosphorylation of tyrosine in such substrates modifies their functions and whether any changes in function can explain the transformed phenotype.